25 June 2018

A happy ending to a diagnostic dilemma.

NOTE: These blog posts are written from the perspective of a GP colleague who still seems to accumulate a list of unanswered questions at the end of each day in practice.  Each post describes how I went about trying to answer the specific questions.  These posts are not intended to be used for specific clinical guidance but hopefully provide links to some useful resources which the registrar can explore for themselves.  

Not long ago a patient came in with a challenging skin problem – an erythematous skin lesion which had been present for months and was very slowly enlarging. It wasn’t itchy and it didn’t look scaly. It felt slightly thickened – dermal rather than epidermal. It was uniformly erythematous and did not have an obvious active edge like many rashes. It was flexural and 4-5cm across.

My first inclination was that it was granuloma annulare but, as is often the case in dermatology, it wasn’t “typical”. It didn’t have the appearance of a normal central area with a raised edge.

This raises the issues of key features of classic cases and, in practice, typical versus atypical presentations.

On the other hand, there is a form of “generalised granuloma annulare” which looks quite like this – but this was a single lesion. However, the likelihood of generalised GA was a little increased because he was diabetic. Was there anything I shouldn’t miss? In the back of my mind was the rare possibility of something like a cutaneous lymphoma.

At its best, general practice is collegial
The patient gave consent for a photo to be shared with colleagues. I asked for opinions and whether anyone could think of anything I might not have thought of. One experienced colleague obviously thought about it and referred me to an AFP article on the best way of doing skin biopsies and she commented it also made her think of Granuloma Annulare as the main possibility.

In the meantime, I did a skin scraping, just in case it showed an unsuspected fungal infection and I checked with a UV light for any fluorescence suggestive of erythrasma – negative. I looked up some pictures and information on for a bit more detail on GA. This revealed even more variants than I had previously been aware of.

I had booked the patient in with another colleague for a biopsy on one of his excision/procedure days. He commented it didn’t look like typical GA. The patient then let me know that the rash had extended to another patch elsewhere. I started to become concerned that, even if it proved to be GA, it might be very difficult to treat and less likely to resolve on its own as most typical cases have done in my previous experience.

The biopsy was done in the method suggested in the article (ellipse at the edge of the lesion) and the result showed it to indeed be granuloma annulare. The histology reports always sound worse than the rash looks! I asked a dermatology colleague (in passing) about treatment if it proved to be spreading more widely. He said that he had tried nicotinamide previously, sometimes with success, so I did some reading on this. It seems to have been used for quite a while with limited evidence (first report 1983 on one patient) but is possibly less hazardous than some of the other options. It isn’t mentioned in the list of more than a dozen treatments for generalised GA listed in dermnetnz. I suspect the number of treatment options is often an indication that a condition is difficult to treat and that no single treatment works consistently. I rang the patient to let him know the result and ask how it was going. He said that soon after the biopsy was done the lesions started to fade and had now nearly disappeared! A happy and intriguing ending.

As I considered the diagnosis, I had chatted in passing with three colleagues. I had reviewed and updated my knowledge from a reputable online resource and further explored some theories about management (which might be useful in the future). All from the challenge of an atypical presentation.

About our guest blogger
Dr Cathy Regan has worked in GP vocational training for more than 20 years.

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